Transient Deformation and Drag of Decelerating Drops in Axisymmetric Flows

Transient deformation and drag coefficients of decelerating drops in axisymmetric flows are numerically computed. The drag coefficients are compared with those of solid spheres. In the case of drops, the behavior of the drag coefficient is dependent on the deformation and internal circulation of the drops in addition to the factors which are important for solid spheres. These, in turn, are dependent on the gas-based Weber number (Weg) and the Ohnesorge number (Ohl). At the relatively low Weg of 1, when the deformation is small, the drag coefficients are about the same for the solid sphere and drop. When Weg is increased, the deformation increases and the difference increases. At the highest Weg of 100, the drop reaches a point of secondary breakup. In general, oblate shapes result in greater drag and prolate shapes in lower drag relative to the solid sphere. Increasing Ohl, which implies increasing viscous forces in the liquid relative to surface tension forces, leads to less deformation and hence lesser differences between solid and drop drag coefficients for a given We.